1. Field of the Invention
The present invention is related to a light diffusing element that diffuses light output from an optical fiber. The present invention is also related to a light guide for an endoscope that guides illumination light to a portion to be observed, equipped with an optical fiber and the light diffusing element.
2. Description of the Related Art
Endoscope systems for observing tissue within body cavities are widely known. For example, endoscope systems that obtain visible images by imaging using white light to illuminate portions to be observed within body cavities and display the visible images on screens of monitors are in wide practical use.
Light guides for endoscopes for guiding illumination light into body cavities are utilized in the aforementioned endoscope systems. It is possible to utilize laser light sources as light sources for generating the illumination light.
There are cases that laser beams emitted by laser light sources will be harmful to human bodies due to their high power densities, even if the emission amount is low. Accordingly, in the case that a laser light source is utilized as an illumination light source, it is preferable to use a laser having the lowest level safety standard class as possible, from the viewpoint of safety of operating sites. Commonly, light diffusing elements (referred to as “light diffusing elements” or “holographic diffusers”) that diffuse light output from optical fibers are provided in the vicinity of output ends of the optical fibers, in order to decrease the level of the safety standard class. Light emitting surfaces at output surfaces of the light diffusing elements diffuse light, and become a two dimensional light source having a large light emitting area. In such cases, the light emitting surfaces of the light diffusing elements being of sizes corresponding to the outputs of laser beams is a requirement to satisfy safety standards.
Meanwhile, miniaturization of light guides for endoscopes is advancing, for the reasons of improving operability, endurance, and the like.
U.S. Pat. No. 6,569,088 discloses a light diffusing element having a two dimensional shape that maximally utilizes dead space at the distal end layout of a light guide for an endoscope, in order to secure a large light emitting surface for the light diffusing element while miniaturizing the light guide for an endoscope.
However, if the two dimensional size of the light dispersion element is merely increased to be larger than an output end of an optical fiber as in U.S. Pat. No. 6,569,088, there is a problem that light L cannot reach parts of a light diffusing element 93 away from the optical axis of an optical fiber 94, as illustrated in FIG. 12.